The old Nuclear Star Cluster in the Milky Way

By S. Chatzopoulos, T. Fritz, O. Gerhard, S. Gillessen, C. Wegg, R. Genzel, O. P. M. Garching, U. Virginia, U. California, Berkeley. 2014

145 citations recorded by the source corpus.

We derive new constraints on the mass, rotation, orbit structure and statistical parallax of the Galactic old nuclear star cluster (NSC) and the mass of the supermassive black hole. We combine star counts and kinematic data from Fritz et al (2014), including 2'500 line-of-sight velocities and 10'000 proper motions. We show that the difference between the proper motion dispersions sigma_l and sigma_b cannot be explained by rotation, but is a consequence of the flattening of the NSC. We fit the surface density distribution of stars in the central 1000" by a spheroidal cluster with scale ~100" and a much larger nuclear disk component. We compute the two-integral distribution function f(E,Lz) for this density model, and add rotation self-consistently. We find that: (i) The orbit structure of the f(E,Lz) gives an excellent match to the observed velocity dispersion profiles as well as the proper motion and line-of-sight velocity histograms, including the double-peak in the v_l-histograms. (ii) This requires an axial ratio of q= 0.73+-0.04 for r<70" consistent with our determination from star counts. (iii) The NSC is approximately described by an isotropic rotator model. (iv) Using the corresponding Jeans equations to fit the proper motion and line-of-sight velocity dispersions, we obtain best estimates for the NSC mass, black hole mass, and distance M*(r<100")=(8.94+-0.31|stat+-0.9|syst)x10^6Msun, Mbh=(3.86+-0.14|stat+-0.4|syst)x10^6Msun, and R0=8.27+-0.09|stat+-0.1|syst kpc, where the systematic errors estimate additional uncertainties in the dynamical modeling. (v) The combination of the cluster dynamics with the S-star orbits around Sgr A* strongly reduces the degeneracy between black hole mass and Galactic centre distance present in previous S-star studies. A joint statistical analysis with the results of Gillessen et al (2009) gives Mbh=(4.23+-0.14)x10^6Msun and R0=8.33+-0.11kpc.

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Citations in the corpus

Nuclear star clusters (2009, methodology): “Using both photometric and dynamical methods, the results fall within the range between ∼ 2.1 ± 0.7× 107M and 4.2± 1.1× 107M (Schödel et al. 2014a; Feldmeier et al. 2014; Chatzopoulos et al. 2015; Fritz et al. 2016; Feldmeier-Krause et al. 2017b).”
THE SHAPE OF THE INNER MILKY WAY HALO FROM OBSERVATIONS OF THE PAL 5 AND GD–1 STELLAR STREAMS (2016, methodology): “Based on recent measurements of R0 (Chatzopoulos et al. 2015; Bland-Hawthorn & Gerhard 2016; Boehle et al. 2016), we use the constraint R0 = 8.1 ± 0.1 kpc.”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, methodology): “The dynamical mass within 100 arcsec = 4 pc is (8.9 ± 1)×106 M (Chatzopoulos et al. 2015); thus M /L4.”
STARS, GAS, AND DARK MATTER IN THE SOLAR NEIGHBORHOOD (2015, unknown): “Now, R 8.3= kpc (Chatzopoulos et al. 2015) and h 2.5R = kpc (Bovy & Rix 2013).”
AN IMPROVED DISTANCE AND MASS ESTIMATE FOR SGR A* FROM A MULTISTAR ORBIT ANALYSIS (2016, background): “…measurements of the trigonometric parallax of H2O masers in the star forming region Sgr B2 give a value of 7.9±0.8 kpc (Reid et al. 2009), while dynamical modelling of the nuclear star cluster gives a statistical parallax distance to the Galactic Center of 8.27±0.13 kpc (Chatzopoulos et al. 2015).”
The mass distribution and gravitational potential of the Milky Way (2016, methodology): “We take a constraint onR0 from Chatzopoulos et al.(2015).”
The Kerr metric (2014, background): “14)×10(6)M⊙ [159], determined from a combined analysis of individual stellar orbits around the black hole and the dynamics of the nuclear star cluster.”
Greatly Enhanced Merger Rates of Compact-object Binaries in Non-spherical Nuclear Star Clusters (2017, background): “However, there is ample evidence that a substantial fraction of NCs, including the one in the Milky Way, have a non-spherical shape (e.g., Georgiev & Böker 2014; Chatzopoulos et al. 2015; Feldmeier-Krause et al. 2017).”
Made-to-measure models of the Galactic box/peanut bulge: stellar and total mass in the bulge region (2015, background): “According to the latest studies (Chatzopoulos et al. 2015; Reid et al. 2014), we assume a distance to the Galactic Centre (GC) of R0 = 8.3kpc.”
An Update on Monitoring Stellar Orbits in the Galactic Center (2016, background): “From more than 10000 proper motions and more than 2500 radial velocities (Fritz et al. 2016), Chatzopoulos et al. (2015) created a dynamical model of the cluster.”
Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling (2017, background): “The angular size of the Schwarzschild radius (Rs) is ∼ 10 µas for Sgr A* for a distance of 8.3 kpc and a mass of 4.3 × 106 M (e.g. Chatzopoulos et al. 2015), and ∼ 3 − 7 µas for M87 with a distance for 16.7 Mpc (Blakeslee et al. 2009) and a mass of 3 − 6 × 109 M (e.g. Gebhardt et al. 2011; Walsh et…”
A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty (2019, methodology): “The measurement is direct because this can be done for individual stellar orbits, as opposed to using a sample of stars together with a dynamical model like in van de Ven et al. (2006) for the globular cluster ω Cen or in Chatzopoulos et al. (2015) for the Milky Way nuclear cluster.”
IMPROVED ESTIMATES OF THE MILKY WAY’S STELLAR MASS AND STAR FORMATION RATE FROM HIERARCHICAL BAYESIAN META-ANALYSIS (2014, methodology): “This result is in excellent agreement with other recent measurements of R0 (e.g., Ghez et al. 2008; Vanhollebeke et al. 2009; Sato et al. 2010; Chatzopoulos et al. 2015), with a large enough error to encompass the variation in results among different methods.”